1. Field of the Invention
The present invention relates to a planar coil component used as a choke coil or a transformer (e.g., a flyback transformer used in a flyback power supply), etc.
2. Description of the Related Art
Planar choke coils or planar transformers, whose direction of winding axis of a bobbin is horizontal and which can easily be made thin, are used in power supplies of flat panel televisions etc. A high-frequency transformer disclosed in the patent document (Japanese Patent Application Laid-Open No. 9-45550) intends to get sufficient insulation effect and creepage distance between coils and a core (paragraph [0004]). In the high-frequency transformer, coils are composed by giving windings between flanges of a bobbin with flanges, and the winding ends are bound to terminals respectively. An insulative cover is put on the bobbin with flanges from upper part, and after that ferrite cores are inserted to the bobbin with flanges from both sides. The patent document said that the high-frequency transformer is such a composition that the creepage distance between the windings and the side legs of the ferrite cores are longer than thickness of the insulative cover and it allows to omit troublesome work for wrapping insulative tape, therefore the high-frequency transformer can easily be made compact and thin (paragraph [0018]).
The high-frequency transformer disclosed in the patent document is such composition that the creepage distance between the coil (winding) and the core is given by the insulative cover, therefore the insulative cover is essential. On the other hand, from the point of view of reducing parts, it is desirable that the creepage distance can sufficiently be given without the insulative cover.